Well, the first thing you need is to make sure the oil is of the correct type, this is Dexron IIIG. If you use Dexron II it will shift roughly, may judder on 3-4th upchanges and may cause damage eventually. If you use a Dexron III (without the G) you will most likely just get a shudder on some low-throttle upchanges.

IIIG is the correct specifies fluid.

One problem, is that Vauxhall recently stopped selling and using IIIG in their garages and use some other fluid for later models and Dexron II for older ones. As the Omega is supposed to be a factory-filled for life, they stipulate II for topping up, however, the dealer may also misinterperate this as being suitable for a fluid change.

To change the fluid, you need to remove two oil pans from the bottom of the transmission, drain, and replace or clean the filer, then refit the pans with new gaskets, and refill with fluid.

I have sourced the correct Dexron IIIg at a reasonable price from a BMW dealer n 1 l bottles.

Whatever you do, make sure you use the best IIIg oil you can get, and be wary of Vauxhall masterfit playing the guessing game.

I had mine done before the IIIg was discontinued, it was around £200 at the dealer - I think.

The capacity is 8.4 litres, but just over half can be taken out in any one change.

Thanks Sooty just got off the phone from a transmission specialist and was quoted £115 + VAT for a complete system flush and a filter change , but he did not say what fluid he would use, does this sound like a good option .

Thanks again Sooty still need to find out what fluid they use , i think they connect up a machine/pump to the cooler pipes and flush the system so i dont think it will be possable to supply my own fluid.

My 2003, 2.2 Omega had reached 80K miles and was due a major service & cambelt.

Despite the automatic gear box working perfectly, I thought I should get the oil & filters changed as I planned on keeping the car for another 40k miles or so.

I actually printed this topic off and took it to the Vauxhall Main Dealer in Lyndhurst, New Forest and asked if there was an issue with oil specification. They said there was no issue and showed me the service schedule which recommends changing every 40k miles.

The once smooth gear box came back with lumpy & erratic low speed changes. I returned it to the garage and they drove it, and said there was nothing wrong with the changes. I pointed out that I'd been driving the car for the previous 80k miles and was therefore very familiar with its operation, and this was not how it had been the day before the oil change.

They refered me to General Motors DEXRON-VI Global Service-Fill Specification sheet which does state that since 2006, this has been the recommended service fill fluid.

As I explained, this data sheet was of little comfort to me as my once smooth gear box was now irritatingly lumpy. Given that the oil was the only thing which had changed from when the gear box was working perfectly, I requested that they drained the DEXRON-VI and refill it with whatever the original factory fill specification would have been. They said they were unable to do this as Vauxhall now specified DEXRON-VI!

Any further protests from me have been completely ignored, adding great customer service to poor mechanical service!

My advice would be: if it ain't broke, don't fix it, just top the fluid level up as required but don't drain and re-fill!